A simple conversion process of inulin polymer into hydroxymethylfurfural (HMF) was developed using Brønsted acid catalyst (HCl) in the presence of an ionic liquid, 1-octyl-3-methylimidazolium chloride ([OMIM]Cl). In addition, the physicochemical properties of inulin particle and its depolymerixation products were scrutinized. FESEM and XRD diffraction frequency showed that inulin particles are clustered in a granulated formation and their molecular structure is highly amorphous. FT-IR analysis identified five characteristic frequency regions: Region 1; 700-900, Region 2; 900-1,200, Region 3; 1,200-1,350; Region 4; 1,350-1,500, and Region 5; 1,530-1,800 cm.1. HPLC analysis confirmed that the major composition of inulin consists of fructose and glucose. The synthesis of HMF was significantly affected by the Brønsted catalyst and its concentration. Its highest yield (63.1±5.1 dwt%) was achieved at 0.3M HCl in the presence of [OMIM]Cl. No presence of the Brønsted catalyst exhibited negligible HMF yield (2.3±1.1 dwt%). Our results demonstrate that the Brønsted catalyst plays a pivotal role in the catalytic process of HMF synthesis from inulin polymer.